While I was looking for things to do for our last day in Galicia, I have read that Porto do Son is close enough to Santiago and worth to visit.
To be honest, I think it is not necessary to visit there especially. If it is on your way to somewhere else, you can stop and take some pictures but apart from that there is not much to do.
In the entrance of the village, there is a church and then a little bit further there is a small, nice port and a small square with some bars. I think the best part of visiting this place was, it took is to the beach – Playa de Las Gaviotas